Photolithography, an important step in a manufacturing process for a semiconductor device, can be used to form a resist pattern in a resist layer by using an exposure process and a development process. Along with the continuous improvement of chip integration, a feature size of photolithography continues to decrease.
A minimum feature size of photolithography is determined by the resolution (R) of an exposure apparatus. The resolution (R) of an exposure system satisfies the following formula: R=kλ/(NA), where k is a coefficient relating to the exposure process, λ represents a wavelength of the exposure light source, NA is the numerical aperture of the optical system of the exposure apparatus. According to the formula, the resolution of the exposure apparatus can be increased by increasing the numerical aperture of the optical system or by reducing the wavelength of the exposure light source.
For increasing the numerical aperture of the optical system to improve the resolution, due to a rigor demanding of the minimum feature size of the next-generation photolithography technology, a very large optical numerical aperture is required. However, the increasing of the numerical aperture not only complicates the preparation and modulation of the photolithography system, but also restricts the depth of focus of the optical system.
For reducing the wavelength of the exposure light source for improving the resolution, the extreme ultraviolet (EUV) light source is the latest developed light source. An EUV light source can generate an exposure light with a 13.5 nm wavelength. So the usage of an EUV light source in an exposure system can obtain a small feature size of photolithography.
An existing method to produce extreme ultraviolet (EUV) light includes use of laser produced plasma (LPP) radiation mode. A laser beam generated by a laser source may bombard a tin (Sn) target for exciting plasma. The excited plasma can radiate extreme ultraviolet (EUV) light.
A structure of an existing EUV light source can be referred to FIG. 1. The EUV light source includes a tin droplet nozzle 101, a laser source 103, lens unit 105, and a condenser lens 107. The tin droplet nozzle 101 can downwardly eject tin droplets 102. The laser light source 103 can generate a laser beam 104. The laser beam 104 can be convergent after going through lens unit 105. The convergent laser beam can bombard tin droplets 102 to generate plasma. The plasma can radiate extreme ultraviolet light 108. The condenser 107 can collect extreme ultraviolet light 108 and gather the extreme ultraviolet light 108 at the central focus 109.
However, the power of the existing EUV light source is still too low to meet the production requirements.
Accordingly, it desirable to provide an extreme ultraviolet (EUV) light source, an exposure apparatus, and a method for fabricating an integrated rotary structure to at least partially alleviate one or more problems set forth above and to solve other problems in the art.